Wednesday 27 March 2019

Mapping Mountains – Trimble Surveys – Mynydd Twr


22.10.18  Plas Gwyn (SH 524 817)  

Plas Gwyn (SH 524 817)

This hill is perched above the eastern coastline of Ynys Môn and looks out over Traeth Coch (Red Wharf Bay) and across to the forested summit of Mynydd Llwydiarth and the limestone encrusted summit of Bwrdd Arthur.  Prior to my visit I had analysed its summit and bwlch with LIDAR and now wanted an on-site visit to bag its summit and take two data sets; one from where LIDAR gives its high point to be situated and the other at a fence junction where the summit is reported to be situated on the Hill Bagging website.

I parked opposite a public football beside the A 5015 as it makes its way between Pentraeth and Benllech.  After spending the morning and early afternoon visiting four P30s dotted across the south-eastern part of the island, many of which were tucked away with the nearest access being narrow country lanes, it felt unusual to encounter fast moving traffic seemingly hurtling past going who knows where.  After waiting for a number of cars and lorries to pass I made my way over the strip of tarmac and through a kissing gate to instant tranquillity and other worldliness as an enclosed old green lane made its way south-eastward up the lower southern part of this hill.

As height was gained a gate gave access to the manicured grazing field on my left, this stretched out toward the high point of the hill, and with beautiful afternoon blue sky above and a slight warmth, and with no one about, it seemed I had the hill to myself, even sheep were absent.

I followed a boundary fence until a gap gave access to the large field toward where the high point of the hill is situated.  Approaching from the south gave me chance to examine the lay of land as I neared the summit and to me it was relatively obvious where its high point lay, once there I compared my position against the ten figure grid reference that the Trimble gave and it matched the LIDAR summit to within one metre.

Gathering data at the summit of Plas Gwyn (SH 524 817)

Having set the Trimble up and activated it to gather data I walked over to the fence boundary where the high point has been reported to be situated.  This part of the hill rises more steeply compared to where LIDAR gives the summit to be placed.  I spent a number of minutes examining this part of land and decided that a second data set was necessary.

The Trimble set-up position at the summit of Plas Gwyn (SH 524 817)

Once the Trimble had gathered and stored data from the LIDAR summit I set it up on what I judged to be the highest natural land beside the fence and again waited for the allotted data to be gathered.  During this I again examined this part of land and realised that the Trimble was placed on what looked like the remains of an old boundary that is slightly raised, but this is not shown as such on the Tithe map.

Gathering data at the second Trimble set-up position

It was a delight to wait for these two data sets to be collected as the weather was blissful with wisps of high cloud accentuating the blueness of sky.  Once the Trimble was packed away I wandered back down the hill to another gate giving access on to the public footpath and then continued on it toward the Porthllongdy Caravan Site where I met David Bennet.  David didn’t know the name of the hill or the field name where its summit is situated, but said if anyone knew it would be Michael Buckley who owns this land.

David directed me to Rhiwlas; Michael Buckley’s home, where I knocked on several doors, unfortunately no one was in, but I did meet the hedge cutter who kindly gave me a forwarding telephone number to make further enquiries.  Once contacted, Michael gave me the name of Plas Gwyn for the hill, with it taking its name from the farm to its south.        



Survey Result:




Summit Height:  76.1m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 52494 81743 (Trimble GeoXH 6000) (summit relocation confirmed)

Bwlch Height:  41.9m (LIDAR)

Bwlch Grid Reference:  SH 52209 81404 (LIDAR)

Drop:  34.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  44.91% (Trimble GeoXH 6000 summit and LIDAR bwlch)









No comments: